It is narrated from Sayyiduna Sahl bin Hunayf (may Allah be pleased with him) that he asked the Messenger of Allah (peace and blessings be upon him) about a man who comes close to his wife and emits madhi (pre-seminal fluid). He (peace and blessings be upon him) said: "He should wash his private part and perform ablution." It was said: O Messenger of Allah! What if some of it gets on his garment? He (peace and blessings be upon him) said: "He should wash the place where he thinks it has touched."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5568